Electroactive polymer based artificial sphincters and artificial muscle patches

ABSTRACT

Provided are artificial muscle patches, which are adapted to be implanted adjacent a patient&#39;s heart, and artificial sphincter cuffs, which are adapted to be implanted around a body lumen, such as the urethra, the anal canal, or the lower esophagus. The devices of the present invention comprise: (a) one or more electroactive polymer actuators; and (b) a control unit for electrically controlling the one or more electroactive polymer actuators to expand or contract the devices.

STATEMENT OF RELATED APPLICATION

This application is a continuation of co-pending U.S. patent applicationSer. No. 10/142,861, filed May 10, 2002, entitled “Electroactive PolymerBased Artificial Sphincters And Artificial Muscle Patches,” which isincorporated by reference in its entirety herein.

FIELD OF THE INVENTION

The present invention relates to medical devices, and more particularlyto artificial sphincters and artificial muscle patches that are based onelectroactive polymers.

BACKGROUND OF THE INVENTION

Millions of Americans are incontinent. Incontinence is the second mostcommon reason for institutionalization of the elderly, generating costsof several billion dollars per year. Incontinence commonly arises frommalfunction of the urethral sphincter. The urethral sphincter is anexternal sphincter formed about the urethra in both males and femaleswhich, when functioning normally, constricts the urethra and preventsflow of urine from the bladder, except when the bladder is voided duringnormal urination. Unfortunately, a spectrum of medical conditions canresult in improper functioning of the urethral sphincter and lead toincontinence, including surgical injury following transurethralresection or radical prostatectomy, neurologic injury, or direct injuryto the sphincter itself.

There are numerous prior art prosthetic sphincters for selectivelyclosing and opening the urethra to prevent incontinence. These devicestypically incorporate an inflatable cuff which surrounds the urethra,and which is inflated to restrict urine flow in the urethra. Examples ofsuch prosthetic sphincters are seen in U.S. Pat. Nos. 4,222,377, and5,562,598. These patents describe devices having an inflatable urethralcuff, a balloon reservoir/pressure source, and a pump. The cuff istypically implanted around the bladder neck in women, and around thebulbous urethra in most men. The implanted cuff functions similarly to ablood pressure cuff.

Fecal incontinence, like urinary incontinence is a debilitatingcondition affecting tens of thousands of Americans. Fecal incontinencein both men and women is typically caused by neurological or musculardysfunction of the anal sphincter, and is commonly the result of trauma.

As with urinary incontinence, prosthetic sphincters for selectivelyclosing and opening the anal canal to prevent fecal incontinence havebeen developed. One such sphincter, which is approved for use by theFDA, is available from American Medical Systems under the name Acticon™Neosphincter. As with the above artificial sphincters for urinaryincontinence, these devices incorporate an inflatable cuff thatfunctions similar to a blood pressure cuff and is inflated to restrictfecal flow. These devices also include a balloon reservoir/pressuresource and a pump.

The above artificial urethral and anal sphincters, however, arecumbersome and limited, and complications occur in a high percentage ofpatents. Moreover, because the system is a pressurized system, it isvulnerable to leakage of the pressurized fluid.

These and other drawbacks of prior art artificial urethral and analsphincters are addressed by a first aspect of the present invention, inwhich an artificial sphincter is provided that is based on electroactivepolymers under electronic control.

Gastro-esophageal reflux disease (GERD) is a condition characterized bythe reflux of stomach contents, including stomach acid, into theesophagus. Approximately 5 million people in the United States aloneexperience chronic GERD. Of these, approximately 60-65% suffer fromlower esophageal sphincter dysfunction, which is typically characterizedby a weakening of the lower esophageal sphincter.

The lower esophageal sphincter is a ring of smooth muscle at the bottomfew centimeters of the esophagus. In its resting state, the loweresophageal sphincter creates a region of high pressure at the orifice tothe stomach. This pressure is critical to the proper operation of thelower esophageal sphincter.

The lower esophageal sphincter opens in response to the peristalticmotion that is triggered when food or beverage enters the esophagus.After food passes into the stomach, the peristaltic motion ceases, andthe lower esophageal sphincter returns to its normal resting state toprevent reflux of the stomach contents, including stomach acid, backinto the esophagus.

Current treatment options for GERD include various endoscopic,laproscopic and pharmaceutically-based therapies, such asfundoplication, RF ballooning, and powerful acid suppressingpharmaceuticals such as Zantac® (ranitidine), Tagamet® (cimetidine) andPepcid® (famotidine). While these options offer a highly focusedtherapeutic potential, they fail in providing a long-term cure, and arenot conducive to patient comfort.

As such, the need for a more dynamic and versatile option for thelong-term treatment of GERD is apparent. To that end, in another aspectof the present invention, an artificial lower esophageal sphincter isprovided, which is based on electroactive polymers that are underelectronic control.

Congestive heart failure is a progressive and debilitating illness. Thedisease is characterized by a progressive enlargement of the heart. Asthe heart enlarges, it is required to perform an increasing amount ofwork in order to pump blood with each heartbeat. In time, the heartbecomes so enlarged that it cannot adequately supply blood. An afflictedpatient is fatigued, unable to perform even simple exerting tasks, andexperiences pain and discomfort.

Millions of Americans suffer from congestive heart failure, witheconomic costs of the disease having been estimated at tens of billionsof dollars annually.

Patients suffering from congestive heart failure are commonly groupedinto four classes (i.e., Classes I, II, I and IV). In the early stages(e.g., Classes I and II), drug therapy is the most commonly prescribedtreatment. Drug therapy treats the symptoms of the disease and may slowthe progression of the disease. Unfortunately, there is presently nocure for congestive heart failure. Even with drug therapy, the diseasewill progress. Further, the drugs may have adverse side effects.

One treatment for late-stage congestive heart failure is hearttransplant.

However, even if the patient qualifies for transplant and a heart isavailable for transplant, it is noted that heart transplant proceduresare very risky, invasive, expensive and only shortly extend a patient'slife. For example, prior to transplant, a Class IV patient may have alife expectancy of 6 months to one-year. Heart transplant may improvethe expectancy to about five years. Similar risks and difficulties existfor mechanical heart transplants as well.

Another technique for the treatment for late stage congestive heartfailure is a cardiomyoplasty procedure. In this procedure, thelatissimus dorsi muscle (taken from the patient's shoulder) is wrappedaround the heart and electrically paced synchronously with ventricularsystole. Pacing of the muscle results in muscle contraction to assistthe contraction of the heart during systole. However, even thoughcardiomyoplasty has demonstrated symptomatic improvement, studiessuggest the procedure only minimally improves cardiac performance.Moreover, the procedure is highly invasive, expensive and complex,requiring harvesting a patient's muscle and an open chest approach(i.e., stemotomy) to access the heart.

Recently, a new surgical procedure, referred to as the Batistaprocedure, has been developed. The procedure includes dissecting andremoving portions of the heart in order to reduce heart volume. However,the benefits of this surgery are controversial, the procedure is highlyinvasive, risky and expensive, and the procedure commonly includes otherexpensive procedures (such as a concurrent heart valve replacement).Also, if the procedure fails, emergency heart transplant is essentiallythe only available option.

Others have used external constraints such as jackets, girdles, fabricslings or clamps to constrain and remodel the heart and reduce heartvolume. See, e.g., U.S. Pat. No. 6,293,906 (citing numerous referencesincluding U.S. Pat. No. 5,702,343 and Pat. No. 5,800,528) and U.S. Pat.No. 6,095,968. In accordance with an example from the above '906 patent,a cardiac constraint device can be placed on an enlarged heart andfitted snug during diastole; for example, a knit jacket device can beloosely slipped on the heart, the material of the jacket can be gatheredto adjust the device to a desired tension, and the gathered material canbe sutured or otherwise fixed to maintain the tensioning.

As an improvement upon the above and in accordance with a further aspectof the present invention, an artificial muscle patch is provided, whichis based on electroactive polymers that are under electronic control.The artificial muscle patch provides cardiac constraint and, if desired,can be electrically paced (e.g., synchronously with ventricular systole)to improve cardiac performance.

SUMMARY OF THE INVENTION

According to a first aspect of the invention, an artificial sphincter isprovided, which comprises: (a) a cuff that is adapted for placementaround a body lumen, which cuff comprises one or more electroactivepolymer actuators; and (b) a control unit for electrically controllingthe one or more electroactive polymer actuators to expand or contractthe cuff.

The one or more electroactive polymer actuators of the artificialsphincter can beneficially comprise (a) one or more active members, (b)a counter-electrode, and (c) an electrolyte disposed between the activemember and the counter-electrode.

In some preferred embodiments, the active members are disposed upon oneor more substrate layers. The active members can be provided in numerousconfigurations on the substrate layer(s), including nonlinearconfigurations that are capable of exerting force vectors along at lasttwo axes, for instance, an S-shaped configuration. The substratelayer(s) can be insulating or conductive in nature. Where insulating, itmay be preferred to provide conductive lines on the substrate layer(s)to allow electrical communication between active members and the powersource.

In certain embodiments, the cuff will further comprise a barrier layerand/or a mesh layer.

The action of the artificial sphincter of the present invention can becontrolled using a variety of control units, for example, (a) powersource and a simple switch or (b) power source and a logic/controldevice such as a computer.

In some embodiments, the cuff is provided with a restoring force tobring it into an expanded or a contracted state, preferably by includingat least one elastic structural element within the cuff to supply such arestoring force. For example, the artificial sphincter cuff can beprovided with an elastic annular tube structure whose length increasesupon a decrease in its cross-sectional diameter.

The artificial sphincters of the present invention can also comprise asensing system (such as a system comprising strain gauges) for sensingthe degree of contraction of the electroactive polymer actuators.

Opposing ends of the artificial sphincter cuffs of the present inventionmay be provided with fasteners for securing the cuff around the bodylumen.

The artificial sphincter cuffs of the present invention may be adaptedfor placement around a number of body lumens, including the urethra, theanal canal, and the lower esophagus.

A lower esophageal sphincter in accordance with the present inventioncan be provided, for example, with sensing system that detects when foodor beverage enters the esophagus, or with a sensing system that detectswhen the stomach is attempting to regurgitate its contents.

Other embodiments are directed to the treatment of fecal incontinence,urinary incontinence or gastro-esophageal reflux disease by implantinginto a patient an artificial sphincter in accordance with the presentinvention.

One advantage of this aspect of the present invention is that artificialsphincters are provided, which address fecal or urinary incontinence ina patient.

This aspect of the present invention is also advantageous in that anapparatus is provided, which offers a relatively instantaneous way toempty the bladder/lower bowel.

This aspect of the present invention is further advantageous in thatartificial urethral and anal sphincters are provided, which are based onelectroactive polymers under electronic control. As a result, apressurized system such as that used in the prior art, with concomitantvulnerability to leakage of the pressurized fluid, is avoided.

Another advantage of this aspect of the present invention is that anartificial lower esophageal sphincter is provided, which compensates forlower esophageal sphincter dysfunction in a patient.

Another advantage this aspect of the present invention is that along-term cure for GERD is provided.

A further advantage of this aspect of the present invention is that anartificial lower esophageal sphincter is provided, which is based onelectroactive polymers under electronic control.

According to another aspect of the present invention, an artificialmuscle patch is provided, which is adapted to be implanted adjacent apatient's heart. The artificial muscle patch comprises: (a) one or moreelectroactive polymer actuators; and (b) a control unit for electricallycontrolling the one or more electroactive polymer actuators to expand orcontract the artificial muscle patch.

As above, the one or more electroactive polymer actuators of theartificial muscle patch can beneficially comprise (a) one or more activemembers, (b) a counter-electrode, and (c) an electrolyte disposedbetween the active member and the counter-electrode. In some preferredembodiments, the active members are disposed upon one or more substratelayers. The active members can be provided in numerous configurations onthe substrate layer(s), including nonlinear configurations that arecapable of exerting force vectors along at last two axes, for example,an S-shaped configuration. The substrate layer(s) can be insulating orconductive in nature. Where insulating, it may be preferred to provideconductive lines on the substrate layer(s) to allow electricalcommunication between active members and the power source. In certainembodiments, the patch will also further comprise a barrier layer and/ora mesh layer.

The action of the artificial muscle patch of the present invention canbe controlled using a variety of control units, for example, (a) a powersource and a simple switch or (b) power source and a logic/controldevice such as a computer.

The artificial muscle patch can further comprise a sensing system fordetecting a patient's heartbeat, in which case the control unitpreferably paces the contraction and expansion of the electroactivepolymer actuators with the heartbeat.

Alternatively, the control unit can pace both the heart as well as thecontraction and expansion of said electroactive polymer actuators.

Other embodiments are directed to the treatment of congestive heartfailure by implanting into a patient an artificial muscle patch inaccordance with the present invention.

One advantage of this aspect of the present invention is that anartificial muscle patch is provided, which is based on electroactivepolymers under electronic control.

Another advantage of this aspect of the present invention is that adevice is provided, which can supply cardiac constraint and, if desired,can be electrically paced to improve cardiac performance.

A further advantage of this aspect of the present invention is that adevice is provided, which can supply cardiac constraint via a procedurethat is considerably less invasive and more simplified that many priorart techniques for surgically addressing congestive heart failure.

These and other embodiments and advantages will become immediatelyapparent to those of ordinary skill in the art upon review of theDetailed Description and claims to follow.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an actuator useful in the presentinvention;

FIG. 2A is a schematic plan view of an artificial sphincter cuff inaccordance with an embodiment of the invention;

FIG. 2B is a schematic cross-sectional view of the artificial sphinctercuff of FIG. 2A, taken along ling A-A′;

FIGS. 3A-3D are schematic plan views illustrating active membersdisposed on a substrate layer in various possible layouts, in accordancewith several embodiments of the invention;

FIG. 4 is a schematic partial plan view of an artificial sphincter cuffin accordance with another embodiment of the invention, whichillustrates snap portions useful for securing opposite ends of thesphincter cuff to one another;

FIGS. 5A-5C are alternate schematic cross-sectional views of theartificial sphincter cuff of FIG. 2A taken along line A-A′, inaccordance with various embodiments of the invention;

FIGS. 6A and 6B are schematic perspective views illustrating thedeployment, within a man and a woman, respectively, of an artificialurethral sphincter, in accordance with embodiments of the invention;

FIGS. 7A and 7B are schematic perspective views illustrating thedeployment, within a man and a woman, respectively, of an artificialanal sphincter, in accordance with embodiments of the invention;

FIGS. 8A-8C are schematic perspective views illustrating the deploymentof artificial lower esophageal sphincters within a patient, inaccordance with various embodiments of the invention;

FIG. 9A is a schematic perspective view illustrating the deployment uponthe heart of an artificial muscle patch, in accordance with anembodiment of the invention; and

FIG. 9B is a schematic cross-sectional view of the artificial musclepatch of FIG. 9A, taken along line A-A′.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to medical devices, such as artificialsphincters and artificial muscle patches, which are operated usingelectroactive-polymer-based actuators.

Electroactive polymers, also referred to as “conductive polymers” or“conducting polymers,” are characterized by their ability to changeshape in response to electrical stimulation. They typically structurallyfeature a conjugated backbone and have the ability to increaseelectrical conductivity under oxidation or reduction. Some commonelectroactive polymers are polyaniline, polypyrrole and polyacetylene.Polypyrrole is pictured below:

These materials are typically semi-conductors in their pure form.However, upon oxidation or reduction of the polymer, conductivity isincreased. The oxidation or reduction leads to a charge imbalance that,in turn, results in a flow of ions into or out of the material in orderto balance charge. These ions, or dopants, enter the polymer from anionically conductive electrolyte medium that is coupled to the polymersurface. If ions are already present in the polymer when it is oxidizedor reduced, they may exit the polymer.

It is well known that dimensional changes may be effectuated in certainconducting polymers by the mass transfer of ions into or out of thepolymer. For example, in some conducting polymers, the expansion is dueto ion insertion between chains, whereas in others interchain repulsionis the dominant effect. Thus, the mass transfer of ions both into andout of the material leads to expansion or contraction of the polymer.

Currently, linear and volumetric dimensional changes on the order of 25%are possible. The stress arising from the dimensional change can be onthe order of 3 MPa, far exceeding that exerted by smooth muscle cells.

Referring now to FIG. 1, an actuator 10 is shown schematically incross-section. Active member 12 of actuator 10 has a surface coupledwith electrolyte 14 and has an axis 11. Active member 12 includes aconducting polymer that contracts or expands in response to the flow ofions out of, or into, the active member 12. Ions are provided byelectrolyte 14, which adjoins member 12 over at least a portion, and upto the entirety, of the surface of active member 12 in order to allowfor the flow of ions between the two media. Many geometries areavailable for the relative disposition of member 12 and electrolyte 14.In accordance with preferred embodiments of the invention, member 12 maybe a film, a fiber or a group of fibers, or a combination of multiplefilms and fibers disposed so as to act in concert for applying a tensileforce in a longitudinal direction substantially along axis 11. Thefibers may be bundled or distributed within the electrolyte 14.

Active member 12 includes an electroactive polymer. Many electroactivepolymers having desirable tensile properties are known to personsskilled in the art. In accordance with preferred embodiments of theinvention, active member 12 is a polypyrrole film. Such a polypyrrolefilm may be synthesized by electrodeposition according to the methoddescribed by M. Yamaura et al., “Enhancement of Electrical Conductivityof Polypyrrole Film by Stretching: Counter-ion Effect,” SyntheticMetals, vol. 36, pp. 209-224 (1988), which is incorporated herein byreference. In addition to polypyrrole, any conducting polymer thatexhibits contractile properties may be used within the scope of theinvention. Polyaniline is another example of such a usable conductingpolymer.

From an energy standpoint, it may be preferable to configure the devicesof the present invention such that the electroactive polymers constrictwhere no potential is applied (i.e., under steady state conditions) andexpand upon the application of an appropriate voltage, or vice versa.For example, the electrolyte composition can frequently be modified toachieve the desired steady-state configuration (e.g., by selectingappropriate ionic species and/or ionic species concentration). However,other actuators types are clearly appropriate.

Electrolyte 14 may be a liquid, a gel, or a solid, so long as ionmovement is allowed. Moreover, where the electrolyte 14 is a solid, itshould move with the active member 12 and should not be subject todelamination. Where the electrolyte 14 is a gel, it may be, for example,an agar or polymethylmethacrylate (PMMA) gel containing a salt dopant.Where the electrolyte is a liquid, it may be, for example, a phosphatebuffer solution, potassium chloride, sodium chloride, or fluorinatedorganic acids. The electrolyte is preferably non-toxic in the event thata leak occurs in vivo.

Counter-electrode 18 is in electrical contact with electrolyte 14 inorder to provide a return path for charge to a source 20 of potentialdifference between member 12 and electrolyte 14. Counter-electrode 18may be any electrical conductor, for example, another conductingpolymer, a conducting polymer gel, or a metal such as gold. In order toactivate actuator 10, a current is passed between active member 12 andcounter-electrode 18, inducing contraction or expansion of member 12.Additionally, the actuator preferably has a flexible barrier layer forseparating the electrolyte from an ambient environment.

Additional information regarding the construction of actuators, theirdesign considerations, and the materials and components that may beemployed therein, can be found, for example, in U.S. Pat. No. 6,249,076,assigned to Massachusetts Institute of Technology, and in Proceedings ofthe SPIE, Vol. 4329 (2001) entitled “Smart Structures and Materials2001: Electroactive Polymer and Actuator Devices (see, in particular,Madden et al, “Polypyrrole actuators: modeling and performance,” at pp.72-83), both of which are hereby incorporated by reference in theirentirety.

Referring to FIG. 2A, an artificial sphincter cuff 100 is illustrated inaccordance with one embodiment of the present invention. The artificialsphincter cuff 100 is adapted to be wrapper around a body lumen ofinterest, whereupon opposing ends of the artificial sphincter cuff aresecured to one another. For example, in the embodiment of the inventionillustrated in FIG. 2A, the artificial sphincter cuff is equipped withholes 102 (one numbered), which allow the device to be laced in placeafter wrapping around a lumen of interest, for example, using suturematerials.

Of course, numerous other embodiments for securing the opposing ends ofthe artificial sphincter cuff 100, other than the embodiment of FIG. 2A,are possible. For example, as illustrated in FIG. 4, snaps can be used.Male snap portions 103 m (one numbered) are provided on one end, whilefemale snap portions 103 f (one numbered) are provided on the oppositeend. By using a series of snaps on one end (for example, two rows offemale snap portions 103 f are provided in FIG. 4), the tension of theartificial sphincter in its initial position can be adjusted. Stillother alternate embodiments are possible, including other securingsystems having male-female components (e.g., plastic ratchet mechanismslike those commonly used in connection with electronic wire tiewrappers). Alternatively, the device can be provided with suture holesat various points along its length for suturing the device into place.

The actuators can be disposed within the artificial sphincter cuffs ofthe present invention in a number of ways. For example, the actuatorscan be separately manufactured and subsequently attached to theartificial sphincter. Alternatively, the actuators can be integratedinto the device, for example by disposing arrays of active members uponone or more sheets of substrate material.

One specific configuration is illustrated in FIG. 2B, which is across-section taken along line A-A′ of the device of FIG. 2A. FIG. 2Billustrates a substrate layer 110 upon which several active members 112(one numbered) are disposed, for example, by a transfer printing ordeposition processes (including electrodeposition or vacuum depositiontechniques). An electrolyte-containing layer 114 is disposed over theactive member(s) 112, and a counter-electrode 118 is in turn disposedover the electrolyte-containing layer 114. Barrier layer 120 and meshlayer 122 are provided over counter-electrode 118. In this way, thedevice 100 is configured in the form of a thin-film, tape-likestructure, enabling a low profile delivery around the body lumen ofinterest.

A plan view of the substrate layer 110 with active members 112 of FIG.2B is illustrated in FIG. 3A. In this figure, nine active members 112(one numbered) are shown disposed on the substrate layer 110. Thenonlinear, s-shaped configuration of the active members 112 allows for acontraction force having force vectors along two axes, for example,horizontal and vertical vectors.

Of course, the active members 112 can be disposed on the substrate layer110 in any number of configurations. For example, FIG. 3B illustrates asubstrate 110 that has twelve diagonal active members 112 (one numbered)disposed upon it. This configuration results contraction forces havingboth vertical and horizontal vector components. FIG. 3C, on the otherhand, illustrates seven active members 112 (one numbered) disposed on asubstrate 110. In contrast to the configurations of FIGS. 3A and 3B,however, the configuration illustrated in FIG. 3C results in contractionforces having a predominantly horizontal component.

Multiple layers of actively members 112 are also possible. For example,it is possible to combine a substrate layer 110 having horizontal activemembers 112 like that illustrated in FIG. 3C with a substrate layer 110having vertical active members 112 like that illustrated in FIG. 3D, toprovide a contraction force having both horizontal and vertical vectors.

As discussed above, beneficial materials for use in the construction ofthe active members 112 include electroactive polymer materials known inthe art such as polyaniline, polypyrrole, and polyacetylene.

To allow operation of the active members 112, the active members 112 andthe counter-electrode 118 are typically connected to the appropriateterminals of a voltage source using any appropriate electricalconnector. In other embodiments, however, it may be desirable to connectonly one of (a) the active members 112 or (b) the counter-electrode tothe power source, while grounding the other of (a) and (b), using thebody as a ground, for example.

Where the active members are controlled as a group, a simple switch canbe used as a control unit to activate them. Where individual control isdesired, on the other hand, each active member is preferably incommunication with, and is individually controllable by, a computer orother suitable control unit. This allows the control unit toindividually perform operations on each active member for the purpose ofeffecting changes to the configuration of the overall device, forexample, as a function of time.

The active members may be in direct communication with the control unitby means of individual dedicated circuits linking each of these elementsto the control unit. Alternatively, it is also possible to place eachactive member is in communication with the control unit using a commoncommunications cable. The signals to each active member are typicallyanalog. If need be, digital-to-analog or analog-to-digital convertersmay be provided to convert the signals from one format to the other. Thesignals to each active member may be conveniently managed andtransmitted over a common cable by multiplexing. Multiplexing schemesthat may be used for this purpose include frequency-divisionmultiplexing, wave-division multiplexing, or time-division multiplexing.Suitable multiplexers and demultiplexers can be employed at each end ofthe cable and along its length at the position of each actuator.

Numerous types of electrical connectors are possible. For example,distinct electrical cables can be connected to the active member of eachactuator. Alternatively, the electrical connections can be printed ontoa sheet. As one example, electrically conductive lines (e.g., lines ofconductive polymer, doped polymer, or metal) can be printed onto a sheetcontaining the active elements, such as an insulating substrate layer110. Such a sheet is analogous to a flexible printed circuit board inthat the necessary elements are printed upon a flexible substrate. Forexample, the printed lines can include a central cable with individualtrack wires extending from the central cable to each active member 112.As discussed above, if individual activation of the actuators isdesired, the cable can be activated, for example, using an appropriatemultiplexing scheme. On the other hand, if the active members are to beactivated simultaneously, the central cable can then simply beactivated, for example, by a switch.

Electrical interconnect wiring can also be provided on a layer that isseparate from the layer containing the active members 112, for example,using plated through-holes or vias (these can also function as “rivets”to hold the composite together). These through-holes can tie, forexample, into a series of conductive track wires disposed on theinterconnect layer, which track wires connect to a “spinal cord”, suchas a cable bundle, flat cable or ribbon cable that runs through thedevice.

It is also possible to use a conductive material as the substrate layer110, particularly where the active members are to be activatedsimultaneously. The conductive substrate layer 110 can in turn beconnected directly or indirectly to the power source or ground. Such anembodiment allows for the efficient distribution of power within thedevice, particularly where a highly conductive substrate material suchas a metal foil is used as the substrate layer 110.

Although not illustrated in FIG. 2B, it may be desirable to provide abarrier layer between the substrate layer 110 and the outsideenvironment, particularly where a conductive substrate layer 110 isused.

Polymeric materials preferred for use in the construction of thesubstrate layer 110 are biocompatible, biostable polymers (i.e.,polymers that do not substantially degrade in vivo). Preferredbiocompatible, biostable polymers include numerous thermoplastic andelastomeric polymeric materials that are known in the art. Polyolefinssuch as metallocene catalyzed polyethylenes, polypropylenes, andpolybutylenes and copolymers thereof; ethylenic polymers such aspolystyrene; ethylenic copolymers such as ethylene vinyl acetate (EVA),ethylene-methacrylic acid and ethylene-acrylic acid copolymers wheresome of the acid groups have been neutralized with either zinc or sodiumions (commonly known as ionomers); polyacetals; chloropolymers such aspolyvinylchloride (PVC); fluoropolymers such as polytetrafluoroethylene(PTFE); polyesters such as polyethylene terephthalate (PET);polyester-ethers; polysulfones; polyamides such as nylon 6 and nylon6,6; polyamide ethers; polyethers; elastomers such as elastomericpolyurethanes and polyurethane copolymers; silicones; polycarbonates;and mixtures and block or random copolymers of any of the foregoing arenon-limiting examples of biostable biocompatible polymers useful formanufacturing the medical devices of the present invention.

Among the more preferred biostable polymeric materials are polyolefins,polyolefin-polyvinylaromatic copolymers includingpolystyrene-polyisobutylene copolymers (more preferably copolymers ofpolyisobutylene with polystyrene or polymethylstyrene, even morepreferably polystyrene-polyisobutylene-polystyrene triblock copolymersdescribed, for example, in U.S. Pat. No. 5,741,331, U.S. Pat. No.4,946,899 and U.S. Ser. No. 09/734,639, each of which is herebyincorporated by reference in its entirety) and butadiene-styrenecopolymers, ethylenic copolymers including ethylene vinyl acetatecopolymers (EVA) and copolymers of ethylene with acrylic acid ormethacrylic acid; elastomeric polyurethanes and polyurethane copolymers;metallocene catalyzed polyethylene (mPE), mPE copolymers; ionomers;polyester-ethers; polyamide-ethers; silicones; and mixtures andcopolymers thereof.

Where a conductive substrate layer 110 is desired, preferred materialsinclude metals, such as gold, platinum, silver and titanium, andpolymers, such as those discussed immediately above, which have beendoped with one or more conductive fillers, for example, carbon black.Preferably, these materials are selected to be non-reactive with thechosen electrolyte.

The electrolyte within the electrolyte-containing layer 114 can be aliquid, a gel, or a solid as previously discussed. It is beneficial thatthe active members 112 avoid contact with the counter-electrode 118 toprevent short-circuiting. The characteristics of the electrolyte that isselected may prevent such contact from occurring, particularly in thecase of a solid electrolyte. If not (for example, where a liquid or gelelectrolyte is used), additional measures may be taken to keep theactive members 112 separated from the counter-electrode 118. Forexample, a series of insulating polymer spacers with interstitialelectrolyte can be placed between the active members 112 and thecounter-electrode 118. Similarly the electrolyte may be provided withinpores or perforations of an insulating polymer layer or within theinterstices of a woven layer or mesh of insulating polymer. Beneficialinsulating polymers for this purpose include insulating polymers withinthe polymer list that is provided above in connection the substratelayer 110. PTFE is a specific example.

The counter-electrode 118 may be any electrical conductor, includinganother conducting polymer, a conducting polymer gel, or a metal such asgold or silver.

Barrier layer 120 may be beneficial for several reasons. For example, abarrier layer 120 is provided in many cases to prevent species withinthe electrolyte-containing layer 114 from escaping the device. Ofcourse, in the case where the counter-electrode layer 118 is impermeable(for example, where a gold foil layer is used as a counter-electrode),the barrier layer 120 will not be needed to perform this function.

The barrier layer 120 may also be beneficial in that it can electricallyinsulate the counter-electrode layer 118 from the surroundingenvironment. For example, in many embodiments, it is desirable toconnect the counter-electrode 118 to the appropriate terminal of a powersource. On the other hand, in the absence of an insulating barrier layer120, the counter-electrode layer 118 will be in contact with the body,which may be desirable where the body serves as an electrical ground forthe device.

Preferred materials for the barrier layer 120 include the polymericmaterials discussed above in connection with the substrate layer 110.

The specific cross-section illustrated in FIG. 2B also includes aflexible mesh layer 122, which can be composed of any number ofbiocompatible materials, including metallic or polymeric materials. Themesh layer 122 can serve several purposes. For example, in the event themesh layer is placed adjacent tissue in the patient, fibrotic tissuein-growth can occur, further securing the device to the tissue.

The mesh layer 122 can also act as a structural element that provides amechanical bias to the device 100. For example, an elastic mesh layer122 can be disposed such that it biases the artificial sphincter to itsextended state.

More generally, in some embodiments, the devices of the presentinvention are provided with a restoring force that biases the devicetoward a preselected configuration. In such embodiments, the activemembers are used to move the device away from this preselectedconfiguration. For example, the device can include one or morestructural elements that are sufficiently elastic to restore the deviceto an expanded configuration upon relaxation of the active memberswithin the device. The device can be changed into a contractedconfiguration by simply contracting the active members disposed withinthe device. The mesh layer 122 constitutes but one way in which thisrestoring force may be provided.

The various layers of the device of FIG. 2A are preferably registeredwith one another and the layers are bonded together to form a unitarymass using a number of suitable known techniques. Such techniques mayinclude, for example, lamination, spot welding, the use of an adhesivelayer or a tie layer, and so forth.

Although not illustrated, the edges of the structure of FIG. 2B arepreferably sealed, for example, to avoid release of electrolyte and toavoid electrical edge effects. This can be accomplished in a number ofways. As a specific example, this objective can be achieved by extendingthe substrate layer 110 (if insulating) and the barrier layer 120 beyondthe other components (i.e., beyond the active members 112, electrolytecontaining layer 114, and counter-electrode 118). This allows thesubstrate layer 110 and the barrier layer 120 to be joined to oneanother, forming an encapsulating structure.

In general, the extent of contraction of the devices of the presentinvention will be determined by the voltage of the power supply incombination with the intrinsic position-dependent electrical propertiesof the active member. However, if desired, the devices sphincter may beprovided with one or more sensors, such as piezoelectronic or conductivepolymer strain gauges, to provide electronic feedback concerning theorientation of the device.

In some embodiments, a drug delivery coating (not illustrated) isprovided outside the device for selective, time-dependent, long-termdelivery of therapeutics. Lubricous coatings such as hydrogel coatings(not illustrated) can also be provided on at least a portion of thedevice surface for easier placement.

In instances where two or more layers of active members 112 areemployed, a layer stack like that illustrated in FIG. 5A can be used. Bycomparing this stack with that of FIG. 2B, it can be seen that the upperbarrier layer 120 is replaced with an additional substrate layer 110having attached active members 112 (one numbered). In this particularconfiguration, both substrate layers 110 are insulators, so theadditional substrate layer 110 acts as a barrier layer. The activemembers 112 attached to the upper and lower substrate layers 110 areseparated from a common counter-electrode 118 by electrolyte-containinglayers 114.

Other configurations are also possible. For example, various layers canbe repeated as necessary to yield the final structure. Referring to FIG.5B, for instance, two (or more) sets of the following layers can beimplemented as desired: (a) an insulating barrier layer 120, (b) aconductive substrate layer 110 with active members 112, (c)electrolyte-containing layer 114 and (c) counter-electrode layer 118.

It is noted that devices of essentially constant cross-sectionalthickness have been exemplified in the above embodiments. However, it isdesirable in some embodiments to vary the cross-sectional thickness ofthe device, for example, to better reflect the anatomical contour of thetissue to which the device is attached and/or to affect the manner inwhich the device acts upon that tissue. An example of a device having avariable cross-section is illustrated in FIG. 5C. In FIG. 5C, thevariable cross-section of the device is provided by including asubstrate 110 of variable cross-section. Other layers, or combinationsof layers, can be used to achieve this effect. However, the activemembers 112, which are generally on the order of about 30 microns inthickness, are less useful for this purpose as they typically do notexhibit substantial changes in thickness.

The devices of the present invention are adapted to be surgicallyinserted into the body of a patient. For example, the devices of theinvention can be used as artificial urethral sphincter cuffs to remedyurinary incontinence by providing a substitute for defective urethralsphincter muscles.

Referring now to FIGS. 6A and 6B, an artificial urethral sphincter inaccordance with the present invention may be surgically implanted withina human torso. An artificial sphincter cuff 100 circumscribes urethra130, which extends from the bladder 132 to the outside environment. Inthese embodiments, the voltage source 140 is located within theabdominal cavity, and a switch 142 is located within the scrotum in thecase of a male patient or the labia in the case of a female patient, sothat it may be externally manipulated by pressing it through the skin.Of course, switches that do not require the user to physically contactthem, such as magnetically controlled or radio controlled switches, canalso be used. The voltage source 140, switch 142 and artificialsphincter cuff 100 are electrically interconnected via cables 144.

The artificial sphincter can be implanted within the trunk using eitheran open technique or a laproscopic technique (an endoscopic technique isalso possible) by first making an abdominal incision through the skinoverlying the abdominal cavity. After the urethra 130 is exposed, thecuff 100 is wrapped around it and the ends secured to one another. Thecuff 100 is wrapped, for example, around the bladder neck in most womenand around the bulbous urethra in most males. This implantationprocedure is analogous to prior art artificial sphincter implantationprocedures, in which a cuff is placed around the urethra, a pressurizedsource is placed in the abdominal cavity, and a squeeze pump is placedin the scrotum or labia.

The voltage source 140 may be replaceable, for example by a surgicalprocedure, or rechargeable, for example, by magnetic coupling or byconnecting external leads to the device.

The artificial sphincters of the invention can also be used as analsphincters to remedy fecal incontinence by providing a substitute fordefective anal sphincter muscles. Referring now to FIGS. 7A and 7B, theartificial sphincters are surgically implanted within a human torso suchthat cuff 100 of the artificial sphincter circumscribes the anal canal134. As with the above embodiments directed to the implantation of anartificial urethral sphincter, a voltage source 140 is typically locatedwithin the abdominal cavity, and a switch 142 is preferably locatedwithin the scrotum in the case of a male patient or the labia in thecase of a female patient.

The artificial sphincter can be implanted within the trunk, for example,by making a first incision around the anus to allow the cuff member 100to be implanted around the anal canal 134 and by making a secondincision into the lower abdominal area to implant the voltage source 140and switch 142. This implantation procedure is analogous to prior artartificial anal sphincter implantation procedures, in which a cuff isplaced around the anal canal, a pressurized balloon is placed in theabdominal cavity and a squeeze pump is placed in the scrotum or labia.Such procedures are presently used, for example, in the implantation ofthe Acticon™ Neosphincter, a product of American Medical Systems, Inc.,which the U.S. Food and Drug Administration (FDA) has granted approvalto market in the United States for the treatment of severe fecalincontinence.

Artificial sphincters in accordance with the present invention can alsobe used to reinforce the operation of the lower esophageal sphincter,for example, in patients experiencing chronic GERD. Referring now toFIG. 8A, an artificial sphincter is surgically implanted within a humantorso, such that a cuff 100 of the artificial sphincter circumscribesthe existing lower esophageal sphincter 136, which is found at the endof the esophagus 139 adjacent the stomach 138. A voltage source 140 anda switch 142 (or other control unit) are typically located under thefascia in the vicinity of the peritoneum. In the embodiment illustrated,the voltage source 140, switch 142 and artificial sphincter cuff 100 areelectrically connected via cables 144. The artificial sphincter can beimplanted within the trunk by procedures akin to those used inperforming known fundoplication processes, including both open andlaproscopic procedures.

Although the cuff portion 100 of the artificial sphincter of FIG. 8A (aswell as those of FIGS. 6A, 6B, 7A and 7B above) is preferably of adesign akin to that discussed above in connection with FIGS. 2A and 2B,other designs are possible. For example, referring now to FIG. 8B, anartificial lower esophageal sphincter is illustrated that, like theartificial lower esophageal sphincter of FIG. 8A, includes a cuffportion 100, which is operated by voltage source 140 and switch 142.Leads 143 and cables 144 are provided to connect respective terminals ofthe voltage source 140 with the counter-electrode and the active membersfound within the sphincter cuff 100.

At the core of the cuff 100 illustrated in FIG. 8B is an annular wiremesh tube 115. The wire mesh tube 115 (wire mesh structures of this typeare well known, for example, in the art relating to vascular and otherendoluminal stents) is preferably constructed of an elastic plastic ormetal material, such as nitinol, elgiloy and/or other shape memory metalor polymer. Surrounding the wire mesh tube 115 is a group of activemembers 112 (one numbered), which are preferably disposed on a substratelayer 110 as discussed above in connection with FIG. 2B. Although notillustrated, an electrolyte-containing layer is typically disposedbetween the active members 112 and a counter-electrode. Finally, abarrier layer 120 is provided over the entire assembly.

When the active members 112 are contracted, the diameter of the tubularcross-section of the wire mesh tube 115 is reduced, increasing theoverall length of the tube (much like the children's toy known as the“Chinese finger trap” lengthens as it tightens its grasp on one'sfingers). As a result, the cuff portion 100 is loosened, opening thelumen that it surrounds (i.e., the lower esophagus). Conversely, whenthe active members are relaxed, the tubular cross-section of the wiremesh tube 115 increases (due to its inherent elasticity), shortening theoverall length of the tube 115 and thereby constricting the lumen.

Structures other than the above wire mesh tube 115 can also be used,including compliant tibular ring structures with variable stent-likecell geometry or with a plurality of individual modules configuredradially or spirally, to enable opening and closing functions that areanalogous to a camera aperture. Double annular structures can also beused, for example, where the inside annulus is provided with theelectroactive polymer actuators and the outer annulus is static.

In simpler embodiments, such at those discussed immediately above, theartificial lower esophageal sphincter employs a switch that is operatedby a patient, for example, when the patient wishes to swallow, belch orvomit. The switch can be placed at a position such as under the skin atthe chest or side, where it can be physically operated by the patient orwhere it can be operated by, for example, magnetic or radio control.

In more complex, automated embodiments of the invention one or moresensors provide a computer, or other suitable control unit, withinformation that the computer uses to make a decision as to whether ornot to open the lower esophageal sphincter.

For instance, as noted above, the lower esophageal sphincter normallyopens in response to the peristaltic motion that is triggered when foodor beverage enters the esophagus. After food passes into the stomach,the peristaltic motion ceases, and the lower esophageal sphincterreturns to its normal resting state to prevent reflux of the stomachcontents, including stomach acid, back into the esophagus. In someembodiments of the invention, one or more sensors are provided that arecapable of sensing the peristaltic state of the esophagus. For example,peristaltic motion can be detected by one or more strain gauges. Forexample, piezoelectric sensors can function as strain gauges.Alternatively, electroactive polymers can be used as a signal generatingmaterials for this purpose. Alternatively, the electrical changesassociated with the peristaltic motion of the esophagus can be measuredby inserting one or more electrical sensors into the esophagus. Similarpiezoelectric and electrical sensor technologies have been developed,for example, in connection with heart rate monitoring systems.

The lower esophageal sphincter should also open in response to the needto belch or regurgitate. As with swallowing, one or more sensors (e.g.,piezoelectric sensors) may be provided that are capable of sensing thedeformation of the stomach that is associated with the need to performone of these functions. Alternatively, electrical sensors can be used todetect the associated electrical signals. In the case of regurgitation,pH sensors can also be used, as regurgitation is typically associatedwith a substantial change in pH.

In each case, a computer or other logic device preferably analyzes thesignals from the sensors using an appropriate algorithm. Once it isdetermined by the computer that appropriate conditions are present, acontrol signal is sent to the artificial lower esophageal sphincter toopen it.

Even with the use of sensors, however, it may be preferred to have amanual backup switch that is accessible to the user in the event ofsystem failure. A backup power source, for example one outside the body,may also be desired in the event that the internal power source 140fails. The backup power source can be connected using the sameelectrical circuitry that is discussed above in connection withrecharging the internal power source 140.

Referring now to FIG. 8C, a lower esophageal sphincter system isillustrated that includes the artificial sphincter cuff 100 and thevoltage source 140 illustrated in FIG. 8A. In addition, sensors 145, 146are provided on the esophagus and on the stomach, respectively, whichprovide input to a signal analysis and control unit 148, preferably acomputer. Components that may be provided within the signal analysis andcontrol unit 148 include signal converters (e.g., analog-to-digital anddigital-to-analog converters), signal amplifiers, and or moremicroprocessors.

As an example, the signals from the sensors 145, 146 can be amplifiedand converted into digital signals, as required. Subsequently, thesignals from the sensors 145, 146 are analyzed by the microprocessorusing a suitable algorithm. Upon receipt of an appropriate signal(s)from the sensors 145, 146, an output signal is sent to the cuff portion100 of the artificial sphincter, using any required signal convertersand/or amplifiers, relaxing the cuff portion 100.

Other embodiments of the invention relate to artificial muscles patches,which can, among other things, make up for loss of muscle functionwithin compromised tissue. Referring now to FIG. 9A, a heart 150 isillustrated having affixed thereto an artificial muscle patch 101. Thepatch 101 illustrated occupies an area generally corresponding to theleft ventricle of the heart.

The internal active members 112 (one numbered) are illustrated withhidden lines in FIG. 9A. As with the above artificial sphincter devices,the active members 112 within the artificial muscle patch of FIG. 9A canbe disposed within the patch in a number of ways, including thedisposition of arrays of active members upon one or more sheets ofsubstrate material within the device.

In this connection, a cross-sectional view taken along line A-A′ of FIG.9A is illustrated in FIG. 9B. The cross-sectional view of FIG. 9B isessentially the same as that illustrated in FIG. 2B. FIG. 9B illustratesa substrate layer 110 upon which several active members 112 (onenumbered) are disposed. An electrolyte-containing layer 114 is disposedover the active member(s) 112, and a counter-electrode 118 is disposedin turn over the electrolyte-containing layer 114. Barrier layer 120 andmesh layer 122 are provided over counter-electrode 118. These layers arediscussed in more detail above. In general, the mesh layer 122 is placedadjacent heart tissue in the patient, allowing fibrotic tissue in-growthto occur, further securing the device to the heart tissue.

Although not illustrated, patch 101 can be provided with a series ofsuture holes along its circumference that allow the patch to be suturedto the heart. The sutures can be tightened during diastole, for example,for a tight fit.

Although the patch 101 in FIG. 9A occupies an area outside the leftventricle of the heart, patches in accordance with the present inventioncan be placed over other areas as needed, including the area outside theright ventricle, or any area where the physical properties or the musclecell activity of the heart has been compromised.

Furthermore, in some embodiments, the patch may be configured such thatit completely wraps around the lower portion of the heart. The opposingends of the patch can then be secured to one another using fasteningtechniques such as those discussed above in connection with variousartificial sphincter designs. As with suturing, fasteners can be fittedsnug during diastole.

Because the active members can be deposited on a film of variablethickness, a near-infinite range of 3-dimensional active memberconfigurations can be achieved. For example, the active members can beconfigured in three-dimensional space to push inward on the heart tissuein a fashion akin to that observed with natural heart muscle strands.

The artificial muscles patch 101 of FIG. 9A is placed in electricalcommunication with a control unit 148 (which typically contains a powersupply and some form of control, such as a switch or a computer) viacontrol cables 144.

As previously noted, the active members 112 within the devices of thepresent invention can be either controlled as a group or individuallycontrolled. Where controlled as a group, the active members 112 cansimply be placed in a mode where they are in a constantly contractedstate, allowing the patch to act as a simple cardiac constraint devicein this instance. A simple switch is all that is required for electricalcontrol of the active members in this case.

The active members 112 can also be controlled as a group in a pulsedfashion to approximate the function of heart muscles. In this instance,the control unit will typically include a pacing unit, which can be usedto both pace the heart muscles and the active members of the artificialmuscle patch. Pacing of the artificial muscle patch 101 can, forexample, assist heart contraction during systole.

Alternatively, a sensor (not shown) can be used to determine the naturalpace of the heart. The signal from this sensor (after amplification anddigitization, if required) can be fed into a computer or other logicdevice where it is analyzed (using, for example, an appropriatealgorithm) to determine pacing of the signal that is sent to the activemembers 112 within the artificial muscle patch.

In other embodiments, the active members 112 are all paced in accordancewith the overall heart rate, but are also actuated at slightly differenttimes in accordance with a suitable algorithm. In this case, aspreviously discussed, individual cables can be provided to individuallyactivate the active members 112 or an appropriate multiplexing schemecan be used.

As above, the extent of contraction of the active members will typicallybe determined by the voltage of the power supply in combination with theintrinsic, position-dependent electrical properties of the activemember. However, if desired, the artificial muscle patch may be providedwith a plurality of sensors, such as strain gauges, to provideelectronic feedback concerning the orientation of the device.

Although the present invention has been described with respect toseveral exemplary embodiments, there are many other variations of theabove-described embodiments that will be apparent to those skilled inthe art, even where elements have not explicitly been designated asexemplary. It is understood that these modifications are within theteaching of the present invention, which is to be limited only by theclaims appended hereto.

1. An artificial sphincter, comprising: a cuff that is adapted forplacement around a body lumen, said cuff comprising one or moreelectroactive polymer actuators; and a control unit electricallycontrolling said one or more electroactive polymer actuators to expandor contract said cuff.
 2. The artificial sphincter of claim 1, whereinsaid one or more electroactive polymer actuators comprise (a) one ormore active members, (b) a counter-electrode and (c) an electrolytedisposed between said active member and said counter-electrode.
 3. Theartificial sphincter of claim 2, wherein said one or more active membersare disposed on at least one substrate layer.
 4. The artificialsphincter of claim 3, further comprising at least one barrier layer. 5.The artificial sphincter of claim 4, further comprising an exterior meshlayer.
 6. The artificial sphincter of claim 3, wherein said one or moreactive members are provided in a non-linear configuration.
 7. Theartificial sphincter of claim 3, wherein at least two of said substratelayers are provided.
 8. The artificial sphincter of claim 3, whereinsaid substrate layer is an insulating layer.
 9. The artificial sphincterof claim 8, wherein conductive lines are provided on said substratelayer to allow electrical communication between said one or more activemembers and said power source.
 10. The artificial sphincter of claim 3,wherein said substrate layer is a conductive layer.
 11. The artificialsphincter of claim 1, wherein opposing ends of said cuff are providedwith fasteners for securing said cuff around said body lumen.
 12. Theartificial sphincter of claim 1, wherein said control unit comprises apower source and a switch.
 13. The artificial sphincter of claim 1,wherein said cuff is adapted for placement around the urethra.
 14. Theartificial sphincter of claim 1, wherein said cuff is adapted forplacement around the anal canal.
 15. The artificial sphincter of claim1, wherein said cuff is adapted for placement around the loweresophagus.
 16. The artificial sphincter of claim 15, further comprisinga sensing system for detecting when food or beverage enters saidesophagus.
 17. The artificial sphincter of claim 15, further comprisinga sensing system for detecting when the stomach is attempting toregurgitate its contents.
 18. The artificial sphincter of claim 1,wherein said electroactive polymer actuators comprise an electroactivepolymer selected from the group consisting of polyaniline, polypyrrole,and polyacetylene.
 19. The artificial sphincter of claim 18, whereinsaid electroactive polymer is polypyrrole.
 20. The artificial sphincterof claim 1, wherein said cuff is provided with a restoring force tobring it into an expanded or contracted state.
 21. The artificialsphincter of claim 20, further comprising at least one elasticstructural element, wherein said restoring force is provided by thestructural element.
 22. The artificial sphincter of claim 21, whereinsaid at least one elastic structural element is an elastic annular tubestructure whose length increases upon a decrease in its cross-sectionaldiameter.
 23. The artificial sphincter of claim 1, further comprising asensing system for sensing the degree of contraction of saidelectroactive polymer actuators.
 24. The artificial sphincter of claim23, wherein said sensing system comprises a plurality of strain gauges.25. A method of treating fecal incontinence comprising implanting into apatient the artificial sphincter of claim
 14. 26. A method of treatingurinary incontinence comprising implanting into a patient the artificialsphincter of claim
 13. 27. A method of treating gastro-esophageal refluxdisease comprising implanting into a patient the artificial sphincter ofclaim
 15. 28. The artificial sphincter of claim 1, wherein said controlunit comprises a power source and a computer.
 29. An artificial musclepatch, comprising: one or more electroactive polymer actuators; and acontrol unit electrically controlling said one or more electroactivepolymer actuators to expand or contract said artificial muscle patch,wherein said patch is adapted to be implanted adjacent a patient'sheart.
 30. The artificial muscle patch of claim 29, wherein said one ormore electroactive polymer actuators comprise (a) one or more activemembers, (b) a counter-electrode and (c) an electrolyte disposed betweensaid active members and said counter-electrode.
 31. The artificialmuscle patch of claim 30, wherein said one or more active members aredisposed on at least one substrate layer.
 32. The artificial musclepatch of claim 31, which further comprises at least one barrier layer.33. The artificial muscle patch of claim 32, further comprising anexterior mesh layer.
 34. The artificial muscle patch of claim 31,wherein said one or more active members are provided in a nonlinearconfiguration.
 35. The artificial muscle patch of claim 31, wherein atleast two of said substrate layers are provided.
 36. The artificialmuscle patch of claim 31, wherein said substrate layer is an insulatinglayer.
 37. The artificial muscle patch of claim 36, wherein conductivelines are provided on said substrate layer to allow electricalcommunication between said one or more active members and said powersource.
 38. The artificial muscle patch of claim 31, wherein saidsubstrate layer is a conductive layer.
 39. The artificial muscle patchof claim 29, wherein said control unit comprises a power source and aswitch.
 40. The artificial muscle patch of claim 29, wherein saidcontrol unit comprises a power source and a computer.
 41. The artificialmuscle patch of claim 29, further comprising a sensing system fordetecting a patient's heartbeat, wherein said control unit paces thecontraction and expansion of said electroactive polymer actuators withsaid heartbeat.
 42. The artificial muscle patch of claim 29, whereinsaid control unit paces the heart as well as the contraction andexpansion of said electroactive polymer actuators.
 43. The artificialmuscle patch of claim 29, wherein said electroactive polymer comprisespolypyrrole.
 44. A method of treating congestive heart failure,comprising implanting the artificial muscle patch of claim 29 adjacent apatient's heart.